United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/015 Apr. 1987
v°/EPA Project Summary
Evaluation of Flexible
Membrane Liner Seams
after Chemical Exposure and
Simulated Weathering
William R. Morrison and Linda D. Parkhill
Strength and durability were tested
in presently available seaming systems
for flexible membrane liners (FML). The
seams were exposed to selected, simu-
lated environmental conditions over
short periods of up to 52 weeks. A total
of 37 combinations of supported and
unsupported polymeric sheet materials
joined by various seaming methods
was subjected to 6 chemical solutions,
brine and water immersion, freeze/
thaw cycling, wet/dry cycling, heat
aging, and accelerated outdoor aging.
Effects of these environmental condi-
tions were evaluated using shear and
peel strength tests before and after ex-
posure. The tests were performed
under dynamic load at room tempera-
ture and under static dead load at 50°C.
In addition six NDT (nondestructive
test) methods were evaluated.
This Project Summary was devel-
oped by ER/k's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
A considerable number of laboratory
tests and pilot-scale studies have been
conducted by various Government and
private-sector groups to assess the ef-
fects of chemical waste products on the
integrity of FMLs in hazardous waste
containment facilities. However, little
has been done to assess the perform-
ance of the various types of seams used
in joining the manufactured roll goods
in the factory and the panels seamed in
the field. To learn more about the
strength and durability of seams made
by presently available seaming sys-
tems, the U.S. Environmental Protec-
tion Agency (USEPA) has funded re-
search with the U.S. Bureau of
Reclamation (USBR) to evaluate FML
seams exposed to selected, simulated
environmental conditions over short
periods of up to 52 weeks. The seams
listed in Tables 1 and 2 were subjected
to six chemical solutions, brine and
water immersion, freeze/thaw cycling,
wet/dry cycling, heat aging, and acceler-
ated outdoor aging.
Effects of the environmental condi-
tions in this study were evaluated using
shear and peel strength tests before and
after exposure. The tests were per-
formed under dynamic load at room
temperature, and under static dead load
at 50°C (122°F). In addition to seam test-
ing, six nondestructive test (NDT) meth-
ods were evaluated in this study. The
six NDT methods were:
- Acoustic method - ultrasonic pulse
echo (5 to 15 MHz)
- Acoustic method - continuous wave
resonant frequency (167 kHz)
- Air lance - 345 kPa (50 Ib/in2)
- Vacuum chamber
- Double seam pressurization
- Mechanical point stress
Exposure Methods
For chemical immersion, solutions
were chosen to represent a wide range
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Table 1. Types of Factory Seams Evaluated
Lining
Material
Scrim
reinforcement
Seaming
method
Seam
width (in)
36-mil CPE
36-mil CPE
30-mil CSPE
36-mil CSPE
36-mil CSPE
36-mil CSPE
36-mil CSPE
36-mil CSPE
38-mil EIA
40-mil EPDM
30-mil CPE
30-mil CPE
30-mil LLDPE
30-mil PVC
30-mil PVC
30-mil PVC
6x6 leno polyester
10 x 10 polyester
8x8 polyester
6x6 polyester
10 x 10 polyester
6x6 leno polyester
10 x 10 polyester
10 x 10 polyester
polyester
10 x 10 nylon
Thermal-hot air 2.25
Thermal-hot air 1.00
Thermal-hot air 2.50
Thermal-hot air 3.00
Thermal-hot air 2.00
Thermal-hot air 2.25
Bodied solvent adhesive 3.00
Thermal-dielectric 1.25
Thermal-hot air 2.00
Vulcanized/3/4 in. capstrip 1.50
Solvent adhesive 1.00
Thermal-dielectric 0.75
Thermal-hot wedge 0.62
Solvent adhesive 1.00
Thermal-dielectric 0.75
Thermal-dielectric 0.75
Table 2. Types of Field Seams Evaluated
Lining
Material
36-mil CPE
36-mil CPE
30-mil CSPE
36-mil CSPE
36-mil CSPE
36-mil CSPE
36-mil CSPE
36-mil CSPE
36-mil CSPE
38-mil EIA
40-mil EPDM
30-mil CPE
30-mil CPE
30-mil HOPE
80-mil HOPE
80-mil HOPE
80-mil HOPE
30-mil LLDPE
30-mil PVC
30-mil PVC
30-mil PVC
Scrim
reinforcement
6x6 leno polyester
10 x 10 polyester
8x8 polyester
6x6 polyester
10 x 10 polyester
6x6 leno polyester
10 x 10 polyester
10 x 10 polyester
10 x 10 polyester
polyester
10 x 10 nylon
—
—
—
—
—
—
—
—
—
—
Seaming
method
Bodied solvent adhesive
Solvent adhesive
Bodied solvent adhesive
Bodied solvent adhesive
Adhesive
Bodied solvent adhesive
Solvent adhesive
Solvent adhesive
Solvent adhesive
Thermal-hot air
Gum tape/cement
Solvent adhesive
Solvent adhesive
Extrusion fillet weld
Extrusion fillet weld
Extrusion lap weld
Thermal-hot dual wedge
Thermal-hot wedge
Solvent adhesive
Solvent adhesive
Solvent adhesive
Seam
width (in)
3.00
3.00
4.50
4.50
3.00
3.00
3.00
3.00
3.00
2.00
6.50
3.00
3.50
N/A
N/A
1.75
1.00
0.63
2.00
3.50
3.00
of chemical groups. These solutions
were:
10 percent phenol (organic acid)
10 percent hydrochloric acid (inor-
ganic acid)
10 percent sodium hydroxide (inor-
ganic base)
10 percent methyl ethyl ketone (ke-
tone)
5 percent furfural (aldehyde)
100 percent methylene chloride (halo-
genated hydrocarbon)
Methylene chloride is not soluble in
water; therefore, pure solvent was used
to avoid the problem of phase separa-
tion. Pure chemicals or aqueous chemi-
cal solutions were selected for testing
rather than simulated or actual wastes
from waste sites to simplify verification
of testing procedures. The use of repre-
sentative groups of chemicals also
allows for reasonable interpretation of
the data.
Chemical, brine, and water immer-
sion of seam samples was accom-
plished in covered 170-liter (45-gal) ca-
pacity polypropylene and polyethylene
tanks. These tanks were filled sepa-
rately with each of the liquids and the
seam samples were then suspended in
the liquids. Three tanks of room-
temperature tapwater and six tanks of
saturated sodium chloride brine solu-
tion [three tanks at room temperature
and three at 50°C (122°F)] were also set
up for immersing samples at the USBR
Laboratory. The samples, except for the
room temperature brine, were removed
and tested after 3, 6 and 12 months of
immersion. Due to an error in schedul-
ing, the room temperature brine sam-
ples were only tested after 3 and 12
months of immersion.
The remaining samples were either
placed in running tapwater for 6-month
saturation before beginning freeze/thaw
or wet/dry cycling tests or set aside for
heat aging tests. For heat aging, seam
samples were subjected for periods of
4,8, and 13 weeks to oven-aging at 70°C
(158°F) in an effort to provide an acceler-
ated test of long-term heat effects on
the seam systems. Double-sided expo-
sure of all samples was used to accom-
modate the large number of samples in
minimum space. An advantage of
double-sided exposure over single-
sided exposure was the reduced time
needed to see the effects of the liquids
on the samples. In parallel with the tank
immersions, smaller coupons of the
parent materials were immersed in
small, clear glass jars for periodic
weight and thickness measurements.
The smaller coupons allowed for easier
inspection of the polymeric sheet mate-
rials for obvious excessive degradation,
swelling, or change in color or surface
texture. If any accelerated response was
observed in the coupons, the seam
samples were removed from the larger
tanks before they were destroyed com-
pletely. The ratio of the volume of liquid
to the surface area for each coupon was
6.2 mL/cm2 (40 mL/in2).
Thirty-two representative seam sam-
ples received accelerated outdoor sun-
light exposure testing on accelerated
weathering test machines located at the
Desert Sunshine Exposure Test (DSET)
Laboratories in Phoenix, Arizona. The
machines are capable of tracking the
sun and focusing the sun's rays on the
5-inch-wide seam specimens for opti-
mum UV (ultraviolet) exposure. The ac-
celerated rate of degradation of the sun
exposure is approximately eight times
that of conventional outdoor exposure.
The samples were visually inspected
and photographed after 6 months of ex-
posure. After 1 year of exposure, the
samples were again inspected and pho-
tographed, and then returned to the
USBR where they were tested for peel
strength retention and observed for any
obvious deterioration.
Test Methods
Coupon samples of some parent ma-
terials were measured for weight and
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thickness before immersion. The 21
coupon samples, each with dimensions
of 50 millimeters by 125 millimeters
(2 in by 5 in), were measured after 1, 2,
3, 4, 8, 12, 36, and 52 weeks of immer-
sion.
Initial physical properties were tested
on the unexposed seam samples for all
lining materials. The data collected rep-
resent the virgin materials and seams in
an unexposed state as received from
the factory or the field fabrication.
After completion of the liquid immer-
sions and the required environmental
conditioning intervals, dynamic shear
and peel testing and static dead load
peel testing were performed to deter-
mine changes in physical properties.
The dynamic shear and peel tests were
conducted in accordance with the test
procedures described in ASTM D 4545-
86, "Standard Practice for Determining
the Integrity of Factory Seams Used in
Joining Manufactured Flexible Sheet
Geomembranes."
Test results of exposed seam samples
were compared to the test results of
original unexposed seam samples for
all tests. The mode of failure was evalu-
ated as well as the numerical results of
shear, peel, and dead load in Ibf/in of
seam width.
Several methods are available for
qualitatively testing seams without test-
ing samples from a completed lining
system. These nondestructive test
methods can be used to measure the
continuity of a seam but cannot be used
to quantitatively measure the relative
strength of the joint or the projected fu-
ture performance. These methods
should be used in conjunction with de-
structive methods in a quality assur-
ance program. Table 3 summarizes the
available NOT methods evaluated in
this study.
Results
• Results of the study indicate that no
direct correlation exists between the
seam shear and seam peel strengths.
For example, high shear strength
does not guarantee high peel
strength. The shear test appears to be
more indicative of the strengths and
weaknesses of the parent material,
whereas the peel test is more a meas-
ure of the strengths and weaknesses
of the seam bond.
• Dead load peel testing indicates that
for the most part, no direct correlation
exists between the results of this test-
ing and the dynamic peel testing.
• For supported FMLs, the seam
strength properties within the same
generic group [CPE (chlorinated
polyethylene) or CSPE (chlorosul-
fonated polyethylene) for example]
varied depending on the particular
FML chemical formulation and the
type of scrim (reinforcing fabric).
• Chemical immersion tests indicate
that changes in weight and thickness
of the materials affected occur quite
rapidly.
• In chemical immersion testing the
performance of the FML seams was
that essentially expected, based on
the recommendations of the FML
manufacturer and review of the avail-
able chemical compatibility data.
• Results of the accelerated outdoor
sunlight exposure testing indicate
that the one-year exposure may be
too long, resulting in accelerated
weathering conditions too severe for
some materials.
• Of the three thermal methods used to
field seam HOPE liners, evaluated in
this study, the extrusion lap weld pro-
duced the highest shear and peel
strengths. The extrusion fillet weld
produced a slightly higher shear
strength than the hot dual wedge, but
the peel strengths of these two seams
were nearly identical. In the peel
tests, however, the hot dual wedge
seam exhibited a failure within the
seam area, and the other two field
seams failed at the seam edge.
• Of the two factory seaming methods
used for the unsupported PVC (poly-
vinyl chloride) and CPE liners, the
seams made with the solvent adhe-
sive exhibited higher shear strengths,
whereas those made dielectrically
produced higher peel strength val-
ues. The higher shear strength was
primarily due to the wider factory
seam for the solvent adhesive seam.
In the shear tests, failure occurred in
the parent material. The same was
also true for the peel tests, except for
the PVC solvent adhesive seam,
where the failure occurred within the
seam itself. No appreciable difference
was noted in the performance of the
two seaming methods.
• Studies on the NDT methods indicate
that each method has particular
strengths and limitations as a check
for seam bonding. However,-none of
the methods determine seam
strengths.
• The performance of the individual
seams are summarized in tables for
chemical immersion and other expo-
sure conditions.
Conclusions
• Peel strength of a seam is an impor-
tant property that should be tested
along with the shear strength to eval-
uate the quality of a seaming method
or operation.
• The dead load peel test, as conducted
in this study, was not a valid proce-
dure for evaluating the quality of a
seaming method or operation.
• Generic-type material specifications
are not sufficient to ensure satisfac-
tory performance of FML seams
when used for hazardous waste con-
tainment applications.
• Short-term chemical immersion tests
of up to 6 months may not be of
enough duration to determine the
chemical compatibility of some FML
seams.
• Existing publishing data and manu-
facturers' recommendations on
chemical compatibility of FML materi-
als give a reasonable basis to make
an initial judgment on the expected
performance of seams in a given
chemical environment.
• The 1-year accelerated outdoor sun-
light exposure may be too severe for
some FML materials.
• The two factory seaming methods
evaluated in this study for PVC and
CPE produced satisfactory seams.
• As part of this study, the factory seam
requirements listed in NSF Standard
No. 54 were reviewed for the materi-
als evaluated. Based on the results of
this study, and other USBR studies,
the shear requirements (breaking fac-
tor) are satisfactory, but the peel re-
quirements (peel adhesion) for the
unsupported materials such as CPE
and PVC appear to be low.
• The air lance, vacuum chamber, and
mechanical point stressing work well
on most seam types with some spe-
cific limitations.
Recommendations
• The dead load peel test should be
conducted utilizing a certain percent-
age of the ultimate peel strength. This
will require additional testing to es-
tablish realistic dead load test values
for the various FML seams.
• The specifications for hazardous
waste containment should incorpo-
rate special provisions to ensure a
specific FML formulation for chemical
compatibility with the materials to be
contained.
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Table 3. Recommended NOT Methods Based on This Research
FML
Supported
CSPE
and
CPE
Unsupported
CPE
Unsupported
PVC
Unsupported
HOPE
HDPE-A
LLDPE
Supported
EPDM
and BUTYL
Supported
EIA
Ultrasonic Continuous Double Mechanical
Thickness pulse echo wave resonant Vacuum seam point
(mils) (5-15 MHz) frequency (167 kHz) Air lance chamber pressurization stress
30
36
45
60
20
30 *
20 *
30 *
40 *
20 *
30
40 '
60 *
80
* * *
# * *
# # 4
r
# #
*
* » *
•
* » #
* » *
# *
# *
# *
# *
* #
100 *
30 » *
45 * *
60
38 *
7 m// = 0.0254 mm.
The 120-day immersion period speci-
fied in EPA Test Method 9090,
"Compatibility Test for Waste and
Membrane Liner," should be re-
viewed to ensure that it is of long
enough duration to determine chemi-
cal compatibility.
Additional studies are recommended
to determine if the accelerated
weather test is truly representative of
long-term weathering of FML's for-
mulated for outdoor exposure.
Additional studies are recommended
to develop a method for testing HOPE
seams for environmental stress
cracking.
Studies should be conducted on eval-
uating the thermal-hot air method for
factory seaming PVC and CPE materi-
als. This would provide an opportu-
nity to document the results for future
specification consideration.
The NSF Joint Committee on FMLs
should give consideration to increas-
ing the peel adhesion values for CPE
and PVC and for supported CPE and
CSPE materials.
W. R. Morrison and L D. Parkhill are with U.S. Bureau of Reclamation, Denver,
CO 80225..
Mary Ann Outran is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Flexible Membrane Liner Seams
after Chemical Exposure and Simulated Weathering," (Order No. PB 87-166
526/AS; Cost: $24.9$, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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Environmental Protection
Agency
Center for Environmental Research
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